Trap 1: Temperature and Physisorption

• WRONG assumption: "Since adsorption needs molecules to come to the surface, more temperature helps, so physisorption increases with T."
• CORRECT: Physisorption is exothermic. Le Chatelier: heating shifts equilibrium toward desorption. Physisorption DECREASES with T.
• WRONG assumption: "Chemisorption also decreases with T like physisorption."
• CORRECT: Chemisorption FIRST INCREASES (needs Ea), THEN DECREASES (desorption at high T).

Trap 2: Gold Number Interpretation

• WRONG: "Starch has gold number 25, gelatin has 0.005. Starch's number is 5000× higher, so starch must protect better."
• CORRECT: Lower gold number = better protective colloid. Gelatin is 5000× more protective than starch. Less mass needed = more efficient.

Trap 3: Colloidal Range

• WRONG: "1–100 nm" or "1–500 nm" or "10–1000 nm" for colloidal range.
• CORRECT: Exactly 1 nm to 1000 nm (= 10^{-9} m to 10^{-6} m).

Trap 4: Hardy-Schulze — Identifying the Coagulating Ion

• WRONG: Looking at the total electrolyte charge or the counter-ion.
• CORRECT: Identify the sign of the sol's charge. The coagulating ion has OPPOSITE charge. Then rank by VALENCY of that oppositely-charged ion.
• Fe(OH)_{3} sol is POSITIVE → coagulated by ANIONS → rank anions by valency.
• $As_{2}S_{3}$ sol is NEGATIVE → coagulated by CATIONS → rank cations by valency.

Trap 5: Freundlich Isotherm Validity

• WRONG: "Freundlich isotherm applies at all pressures and predicts saturation."
• CORRECT: Freundlich is valid ONLY at intermediate pressures. It does NOT predict saturation (x/m → ∞ as P → ∞). Langmuir predicts saturation.

Trap 6: Tyndall Effect — Which Systems Show It

• WRONG: "Suspensions also show Tyndall effect since they have large particles."
• CORRECT: Tyndall effect specifically characterizes COLLOIDS (1–1000 nm, particles comparable to light wavelength). Suspensions scatter light differently. TRUE SOLUTIONS do NOT show Tyndall.

Trap 7: Lyophilic vs. Lyophobic Stability

• WRONG: "Both lyophilic and lyophobic colloids coagulate with equal amounts of electrolyte."
• CORRECT: Lyophobic colloids coagulate with SMALL amounts of electrolyte (only charge neutralization needed). Lyophilic need LARGE amounts (must first remove hydration shell, then neutralize charge).

Trap 8: Emulsion Type Confusion

• WRONG: Butter is O/W (seems logical because butter seems to have water in it).
• CORRECT: Butter is W/O (water dispersed in fat). The continuous phase is oil/fat. Hence butter is greasy and does not wash off with water.